High-voltage bushing



April 1, 1924; 1,488,919

- A. B. HENDRICKS, JR

HIGH VOLTAGE BUSHING Filed Jan. 2 1919 Fig. 2.

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UNITED STATES PATENT OFFICE.

ALLAN B. HENDRICKS, JR, OF PITTSFIELD, MASSACHUSETTS. ASSIGNOR TOGENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

HIGH-VOLTAGE nusnmo.

Application filed January 2, 1818. Serial No. 269,288.

To all whom it may concern Be it known that I, ALLAN B. HENDRICKS, Jr.,a citizen of the United States, residing at Pittsfield. in the county ofBerkshire, State of Massachusetts, have invented certain new and usefulImprovements in High-Voltage Bushings, of which the following is aspecification.

My invention relates to high voltage bushings or insulators forelectrical conductors, and has for its object the provision of animproved insulator which is durable, easily manufactured and which maybe made in smaller sizes than known bushings having a similar rating andyet possess desirable electrical characteristics.

Insulators built to withstand high voltages will fail either on accountof c-reepage, arc-over or puncture. It has been custo'1n ary to providethe surfaces of insulators with deep corrugations in order that theremay be sufiicient creepage distance to withstand the electrical strainswithout unduly increasing the length of the insulator.

This arrangement however not infrequently results in an unevendistribution of the electrostatic flux over the surface of the insulatorso that corona will appear even when the insulating material of whichthe insulator is constructed is not strained to anything like theworking limits of its breakdown strength. As a consequence, in reckoningwith these various factors in the design of an insulator, a compromiseresults at the expense of the size and most economical use of materialemployed.

In the practice of my invention I pro vide a principal creepage pathwith interposed barriers in a dielectric medium other than air and inaddition I so control the electrostatic flux distribution that coronadoes not appear disproportionately to the puncturing ualities of thematerials employed, thertihy enabling me to make a better disposition ofthe insulating material than was heretofore known in the art.

For a more complete understanding of the nature and objects of myinvention reference should be had to the following description whentaken in connection with the accompanying drawing, in which Fig. 1showns an insulator partially in section and partially in elevationwhich embodies my invention; while Fig. 2 similarly shows amodified.form of insulator embodylng my invention.

eferring now to Fig. 1 of the drawing, 1.0 denotes a conducting tube,which may be the conductor itself to be led through the bushingstructure, but is preferably only a housing therefor. This conductor isto be insulated from the surrounding conducting structure orsleeve'indicated generally at S. Surrounding the tube 10 is formed aninsulating cylinder 11. This cylinder is preferably formed of somehomogeneous fibrous insulating material such as shellacked paper formedunder heat and stops short of the upper end of the tube 10 by somedistance as shown at 12 while at the lower end it extends beyond the endof the tube preferably a somewhat greater distance, as shown at 13. Theopening at the lower end of cylinder 11 has a conical flare indicated at14 for a reason presently to be described.

About an intermediate portion of the c linder 11 is placed a uniformlayer 15 o a suitable insulating material, which may conveniently be awrapping of varnished calnbric. This layer has its ends slitted for somedistance in an axial direction and folded back to form barriers; theslits being so placed in the superposed layers of the wrapping 'thatthey have a staggered relation, while the barriers are with advantageformed by bending the slitted portions sharply back overthe ends ofsleeve S.

The layer of insulating material 15 isheld in place and fitted snuglyinto the conducting sleeveiS, shown as having a ground shield 16 and aflange or collar 17 formed thereon near the upper end.

The collar 17 affords a means for securing the bushing to the cover orwall of the housing enclosing the electrical apparatus served by thebushing for which purpose the collar is provided with bolt openings asshown at 18.

The slitted ends of the insulating layer loare formed, atthe lower endof sleeve S,

into the barrier or collar 19 which is sup rted in a radial position bythe insulatmg washer 20. This washer 20 is held in place by aninsulating distance sleeve 21 which is tightly wedged between thiswasher and a similar washer 22 supported by insulating dowel pins 24;the latter being partially embedded for support in the cylinder 11.Since the lower end of the bushing is designed to extend beneath thesurface of the oil or other insulating medium in which the electricalapparatus served by the bushing is submerged, all trapped air must bedisplaced from this end of the bushing structure to insure the properdi-electric. strength. T this end the distance sleeve 21 is providedwith openings 21' to permit oil to enter and displace air between it andthe cylinder 11, also cotton yarn or other insulating material willpreferably be inserted at 25 to tightly fill the space between collar 19and washer 20, thus providing a more nearly homogeneous dielectricmedium at this point about the conductor.

The upper end of the insulating layer 15 is partially folded back uponitself but it envelops the extended upper end 16 of the conductingsleeve S, which end 16 serves as an electrostatic shield controlling theelectrostatic flux passing from the tank to the conductor to get a. moredesirable distribution, in a well known manner which is set forth in U.S. Letters Patent to Sieber, No. 1,258,736.

The end 30 is held pressed back in a manner similar to collar 19, bymeans of insulating filling 32 and the superposed insulating distancesleeve 33; the latter being held in place by the pressure exerted by adepending portion 34 of the metallic cap 35. An intervening felt gasket36 is shown for the purpose of taking up a certain amount of compressionand allowing for lost motion of the parts.

The metallic cap rests upon the external insulating cylinder or member37 which rests on collar 17 and forms the upper portion of the bushing.This member is shown as secured between gaskets 38 and 39 in order tomake tight joints both with the cap 35 and the flange 17.

The member 37, when in service, is filled with an insulating compound,preferably petroleum jelly, to a desired height; here indicated at 40.This compound is conveniently introduced through the plug closed opening41 in cap 35. In order that this compound may readily enter on bothsides of the distance sleeve 33. I provide a num ber of openings 33 nearthe top and bottom of the sleeve. which openings also permit air toescape and thus avoid air pockets. For a similar reason the openings 34have been provided in the depending portion 34: of the cap The exteriorcontour of the cap 35 is designed to secure a reduction in concentrationof the electrostatic fiux at the end of the bushing, but obviously thecap may be formed to give any other desired distribution. The portion 34is also formed to assist in securing the desired distribution of thisflux interiorly of the bushing in a manner set forth in U. S. LettersPatent No. 1.350,- 925 issued Aug. 2%, 1920, on an application by G.Faccioli. The cap 35 has a depressed central cup-shaped portion 42arranged to snugly fit about the upper end of tube 10 which protrudesfrom the insulating cylinder 11. This cup-shaped portion 42 contains acompressible helical spring 43 which reacts against the nut or collar 44which is screwed or otherwise secured upon the protruding tip of theconducting tube 10. which construction provides a convenient means forrigidly retaining the whole bushing structure in assembled relation.

Rotatably mounted upon the nut or collar M is the capstan nut 15 whichis rigidly secured to the conducting rod %6 (here shown connected by pin47} which rod passes down inside the tube 10 and serves as theconductor.

The connections to the aerial lead are made on the upper side of the nut45 as indicated at 48.

The lower end. of rod 46 is threaded as shown at 49 for engagement withthe upper end of the lead 50 coming from the electrical apparatus notshown which is housed by the casing on which the bushing is mounted.

The end of the lead 50 is submerged beneath the level of the cooling andinsulating medium. such as oil, and is surrounded by av wrapping 51 ofinsulating material having a tapered formation adapted to fit snuglyinto the flared opening 14 in the cylinder 11. When this lead is drawnup into opening 1i by manipulating the capstan nut 45, the upper end ofthe lead 50 is drawn snugly into and against the lower end of theconducting tube 10 and a connection is afforded having excellentelectrical characteristics enabling the use of an interior bushingstructure having smaller proportions for given ratings than anythingpreviously attempted.

In operation, the creepage surface from either end of the conductingtube 10 to the sleeve S. which may be taken as ground potential, is madegreat. Considering for a moment that from the protruding end shown at12. the creepage path is over the surface of cylinder 11 down to andover the insulating filling at 32, thence over the end folded back at 30to the sleeve S. In like manner the creepage path from the end of tube10 at 13 is made long by means of the washers 20 and 22 on the lowerextremity of cylinder 11. The resistances of these creepage paths aredesignedly so proportioned in length that the bushing will fail in someother manner (preferably by are over) before it will fail by creepage.The bushing, of course, may fail by creepage over or by appearance ofcorona on the surface of insulating member 37, but the cap 35 is preferi being overlaid on t ably so shaped that local concentration ofelectrostatic flux over the surface of member 37 is avoided therebyobtaining approximately uniform distribution of the stress over thesurface of member 37 and substantiall maximum efliciency in theutilization .of t e insulatin The greatest tendency to failure bpuncture is across the space between tube 10 and sleeve S. Thedielectric strength and thickness of cylinder 11 and of layer 15 arepreferably such that failure here is very remote.

The air or dielectric medium exterior to member 37 as a consequenceofiers the weakest path across which failure may take place. The arcingdischarge, in such case, would generally be between the cap 35 and thetop of the housing which supports the bushing. It is thus seen thatfailure by arc-over may take place with my bushing without any permanentinjury to the bushing structure.

The relative insulating strengths of the two ends of a bushing made inaccordance with my invention are preferably so proportioned that theupper end will fail by are over before the lower end. The thickness ofthe insulating material used in the construction is preferably so chosenthat a failure by puncture in my bushing will be the last in order totake place, while the flux control which I have provided enables me, bysuitably proportioning the parts, to prevent corona from appearing atany point before failure from are over is about to occur.

When the electrostatic stress components occurring longitudinally overthe surfaces of the insulating structure, which can safely be employedover the bushing shown in Fig. 1, must be exceeded, a greater surface todistribute such increased stress components is with advantage providedin the manner illustrated in Fig. 2.

In Fig. 2, 110 denotes the '-.conducting tube which contains theconductor to be insulated. About the tube 110 is formed an insulatingcylinder 111; a portion of the tube 110 protruding from the up er end isshown at 112 but stops short of t e lower end as shown at 113. Thecylinder 111 has a flared lower end 114 to snugly receive the lead fromthe winding in the same manner as shown in Fig. 1.

Instead of one la er of insulating material lie cylinder 111, as in Fig.1, I here provide a plurality of layers, two being shown, an inner one115 and an outer one 115' which are surrounded intermediate their endsby the snugly fitting sleeve 116.

' This sleeve has a flange 117 provided with bolt openings 118;

The ends of the layers 115 and 115 are slitted and folded back in asimilar manner to that above described to form collars 119 and 119respectively at the lower ends, which collars are held back by thedistance properties of member 37.

sleeves-121-and 121' respectively; interven ing washers 120 and 120'being here employed to build up a collar of desired thickness. Thedistance sleeves 121 and 121' are shown as provided with openin at topand bottom for the same purpose t at o nings were shown in distancesleeve 21 in ig. 1.

The distance sleeve 121 bears ona washer 123 held in place by theprojecting pins 124 which are secured in the cylinder 111. It isobserved'that sleeve 121' fits between 001-. lars 119 and 119, thelatter being turned back against the lower edge of sleeve 116, and isrigidly supported as well as collar 119 thus forming a ri id lower endconstruction for this form of ushing.

Theconducting sleeve 116 in this bushin is also provided with anelectrostatic shiel 126 over the ed e of which is folded back the'upperslitte end 130' of the insulatin layer 115. The rounded edge of this enis built up by means of the washer and felt construction shown at 131 tosupport the.

distance sleeve 132 interposed betweenz -the end 130' and the collarforming end 130 of the insulating layer 115.

Instead of depending on another distance sleeve to be clamped in lace bythe pressure of the cap on the bushing structure as was done in thefirst described bushing, I have here illustrated an alternateconstruction which is simpler and easier to assemble correctly.

The collar 130 is held down b a somewhat elastic washer 133 which 5 heldin place by the insulating cylinder 134. This cylinder 134 is short and1s slipped over the upper end of cylinder 111 before the u per bushinstructure is put in place an cemente fast to the cylinder 111. Thiscementing may be readily accomplished by applying shellac to fill thespace between the two cylinders and giving the whole a heat treatment.

A metallic cap 135 is slipped about the protrudingend of conducting tube110 to hold the other insulating member 137 in place. This member restsbetween gaskets 138 and 139 to insure ti ht joints to kee the insulatingcompound s own at 140 rom leaking out.

The cap 135 is similar to the cap 35 and has a dependin flux controllingmember 136 and a plug 0 osed opening 141 to admit the insulatingcompound. It is also provided with a cup-shaped formation 142 containingspring 143 which is compressed by nut or collar 144 which engages withthe tip of tube 110 to retain the cap 135 and member 137 in place underpressure. Both the member 136 and sleeve 132 are provided with openings,indicated at 136' and 132' respectively, so that the insulating compoundwill displace the air which would otherwise be pocketed at these points.

Turning in the nut or collar 144 is the capstan nut 145 having athreaded rod or conductor 146 which is to be rotated into threadedengagement with the lead from the electrical apparatus (not shown)similar in manner to that described for Fig. 1.

This construction has not only the advantage of permitting a small lowerend bushing construction but it permits the bushing to be secured to thecover of the housing or tank for the electrical apparatus before thecover is secured in place. When the submerged leads have been properlyplaced, the cover of the tank, carrying the bushings secured in place onit, can be brought into position and fastened to the tank. Theconnections with the submerged leads are then made merely by rotatingthe capstan nuts. All fishing for leads and electrical connections to bemade under the oil or surface of the fluid insulating medium in the tankare thus avoided.

It is obvious that bushings of my invention may be removed from thecover of encased electrical apparatus with equal facility since themanipulation of the capstan nuts is all that is required to disconnectthe bushings from the electrical apparatus.

While I have here shown two embodiments of my invention which are, atpresent, the best means known to me for carrying the same into effect, Iwould have it understood that this is merely illustrative and that I donot mean to be limited thereby to the precise details here disclosedsince obvious alterations thereof will occur to those skilled in thisart, nor in the choice of recognized equivalents except as defined in myclaims hereunto annexed.

lVhat I claim as new and desire to secure by Letters Patent of theUnited States, is

1. In a high voltage bushing structure, the combination with aconductor, of a conducting sleeve, an insulating cylinder surroundingsaid conductor, insulating material overlying the surface of saidcylinder intermediate its ends, said material being snugly fittedbetween said cylinder and sleeve and having its ends formed intobarriers, distance sleeves supporting said barriers in predeterminedpositions, and an exterior insulating member having an insulatingfilling enclosing the barrier structure on one side of said conductingsleeve.

2. A high voltage bushing of the type described comprising a tubularconductor, an insulating structure surrounding the same, and a threadedrod in said tubular conductor having an external manipulating device forrotating said rod into and out of threaded engagement with a cooperatinglead entering said tubular conductor.

3. A high voltage bushing of the type described comprising a tubularconductor, an insulating structure surrounding the same,

and a threaded conducting rod in said tubular conductor having anexternally operable nut rotatable in one end of said tubular conductor,said rod being arranged to be rotated into and out of threadedengagement with a cooperating lead entering the other end of saidtubular conductor.

4. A high voltage bushing of the type described comprising a tubularconductor, an insulating structure surrounding the same, and a threadedconducting rod in said tubular conductor having a capstan nut securedthereto and arranged to turn in one end of said tubular conductor, thethread on said rod being arranged to engage with and hold snugly againstsaid tubular conductor a cooperating lead entering the other end of saidtubular conductor.

5. The combination with a conducting tube, of an insulating cylindersurrounding said tube having a countersunk formation overreaching oneend of said tube, an external insulating structure surrounding the otherend of said tube and cylinder, a conductor in said tube. a winding leadencased in insulation provided with a complementary end formationadapted to fit snugly in the overreaching portion of said cylinder, andmeans operable from the exterior of said tube for uniting said conductorand lead.

6. The combination with a conducting tube, of an insulating cylindersurrounding said tube having a countersunk formation overieaching oneend of said tube, a conducting sleeve surrounding said cylinderintermediate its ends, an external insulating member secured betweensaid sleeve and the other end of said tube, a conductor in said tube, awinding lead encased in insulation provided with a complementary endformation adapted to fit snugly into the overreaching portion of saidcylinder, and means operable from the exterior of said tube for unitingsaid conductor and lead.

7. In a bushing structure the combination with a conducting tube havinan insulating cylinder surrounding said tube having a countersunkformation overreaching one end of said tube, the other end of said tubeprotruding, a conducting sleeve surrounding said cylinder intermediateits ends, layers of insulating material snugly fitted between saidsleeve and cylinder, a conducting cap secured to the protruding end ofsaid tube, and an external insulating member adapted to contain aninsulating filling secured between said cap and sleeve, of a conductingrod in said tube, a winding lead adapted for threaded engagement withsaid rod encased in insulation, said encasing insulation provided with acomplementary end formation adapted to fit snu 1y into the overreachingportion of said cy inder, and means on an exterior portion of said rodoperable for drawing said rod and lead to gether to form an unbrokenexterior insulating surface.

8. In a bushing structure the combination with a conducting tube, havingan insulating cylinder surroundin said tube and overreaching one end ofsai tube and provided with a countersunk formation having a flaredconical bore tapering off toward the end of said tube, the other endprotruding from thecylinder, a conductin sleeve surrounding saidcylinder interme int-e its ends and formed to rovide an electrostaticflux controlling shie d, a conducting cap formed 3 15 to control theflux in conjunction with said sleeve secured to the protruding end ofsaid tube, and an external insulating member adapted to contain aninsulating filling secured between said cap and sleeve, of a conductingrod in said tube having a threaded inner end and a capstan nut on theouter end, and a winding lead provided with en- ALLAN B. HENDRICKS, JR.

